This invention relates to a control system for use in driving a vibratory member, and deals more particularly with such a control system for driving the member at its resonant frequency.
Many machines or devices have members supported for vibration and driven in such vibration by an electromagnetic driver; and often it is desired that such a member be driven at or near its resonant frequency. An example of such device is a vibratory bowl feeder having a bowl supported by springs for movement relative to a base and vibrated relative to the base by one or more electromagnetic drivers. To obtain maximum efficient use of the power applied to such a feeder, and to obtain best performance of the feeding function, it is usually desired that the driver or drivers drive the bowl at its resonant frequency. The driving frequency is typically fixed by the frequency of the power supply, for example 60 Hz, and a match between the driving frequency and the bowl resonant frequency is usually obtained by tuning the bowl to cause it to have a resonant frequency equal to the power supply frequency. This bowl tuning, which may for example be done by adjusting the weight or weight distribution of the bowl or the spring rate of its suspension, is usually a relatively time consuming one. Furthermore, after a bowl is tuned it tends to go out of tune after a period of usage so that to maintain optimum performance the bowl should be frequently retuned.
Also, in many cases the optimum design resonant frequency of the feeder bowl or other member in question is substantially different from the frequency of the available power supply. In the past such mismatches have been troublesome as it has generally been difficult and expensive to provide frequency converters or other devices to energize the driver or drivers at a frequency other than that of the power supply.
The purpose of the invention is, therefore, to provide a control system for use with a driven vibratory member whereby the member is driven at its resonant frequency, so that no exact tuning of the member is required, and whereby the driving frequency follows changes in the member's resonant frequency so that changes in such resonant frequency will not adversely effect the member's performance.
A further object of the invention is to provide a control system for an electromagnetically driven vibratory member wherein the control system may be operated in an open-loop mode and its output frequency adjusted to cause said output frequency to match the member's resonant frequency and wherein the control system may thereafter be operated in a closed loop mode to cause its output frequency to follow changes in the member's resonant frequency.
Another object of the invention is to provide a control system of the foregoing character which may be used with a constant frequency power supply to drive a vibratory member at any desired frequency within a wide range of frequencies.
Another object is to provide a control system for a vibratory drive which is more efficient, which generates less heat and which can be made in a smaller size than presently available control systems serving the same general purpose.
Still another object of the invention is to provide a control system such as aforesaid which may easily and economically be made by using to a large extent components available as standard integrated circuits.
Other objects and advantages of the invention will be apparent from the following detailed description and from the drawing forming a part hereof.